1. Field of the Invention
The present invention relates to a method for depositing a functionally gradient thin film, and more specifically to a method for depositing a compound thin film having a gradient function on a surface of a substrate using a plasma CVD method.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a typical plasma CVD device used in conjunction with a plasma CVD method so as to deposit a thin film on a surface of a substrate.
This plasma CVD device shown in FIG. 1 includes a process chamber 1 in which an internal space is provided so as to serve as a reaction field for depositing a thin film when the internal space is filled with a gas used as a material for the thin film. A pair of first and second parallel-plate electrodes 2 and 3 are provided in the process chamber 1 so as to be respectively positioned in the upper and lower parts of the process chamber 1 and opposed to each other in a parallel manner.
The first parallel-plate electrode 2 provided in the upper part of the process chamber 1 is connected to a high-frequency power source 6 provided outside the process chamber 1. The second parallel-plate electrode 3 provided in the lower part of the process chamber 1 is grounded. Further, the second parallel-plate electrode 3 is used as a mounting board on which a substrate 5 used for depositing a thin film is mounted. The second parallel-plate electrode 3 includes a heater 4 for heating the substrate 5 mounted on the second parallel-plate electrode 3.
A gas introduction line 7 is provided at one side of the process chamber 1 so as to introduce a material gas for depositing a thin film into the process chamber 1. The gas introduction line 7 is connected to a gas cylinder (not shown) or the like which contains the material gas. A gas exhaust line 8 is provided at the other side of the process chamber 1 so as to exhaust the gas from the process chamber 1. The gas exhaust line 8 is connected to a pump (not shown) for pumping the gas from the process chamber 1.
In the case where this plasma CVD device is used for depositing a thin film on a surface of the substrate 5, after the substrate 5 is mounted on the second parallel-plate electrode 3 in the process chamber 1, the gas introduction and exhaust lines 7 and 8 are adjusted so as to control introduction and exhaustion of the material gas, whereby the process chamber 1 is maintained so as to be filled with a prescribed amount of material gas. A high-frequency voltage is applied by the high-frequency power source 6 to the first parallel-plate electrode 2 in the process chamber 1 filled with the prescribed amount of material gas so as to create an electric field between the first and second parallel-plate electrodes 2 and 3. The electric field accelerates decomposition and excitation of the material gas between the first and second parallel-plate electrodes 2 and 3 such that the material gas is in a plasma state between the first and second parallel-plate electrodes 2 and 3, thereby resulting in a plasma space 9 indicated by a dotted line shown in FIG. 1. The plasma created in the plasma space 9 causes a desired thin film to be deposited on the surface of the substrate 5.
In such a thin film deposition method using the plasma CVD device including the pair of first and second parallel-plate electrodes 2 and 3, the material gas is required to be uniformly provided in the plasma space 9 so as to deposit a homogeneous thin film on the substrate 5. However, it is not easy to satisfy this condition when the substrate 5 on which the thin film is deposited has a large surface area. As the pressure of the material gas in the process chamber 1 is increased, the material gas provided in the plasma space 9 becomes notably nonuniform. Accordingly, when depositing the thin film on the substrate 5 having a large surface area, in general, the pressure in the process chamber 1 is reduced. However, by reducing the pressure in the process chamber 1 so as to deposit the thin film on the substrate 5, the deposition rate of the thin film is also reduced (i.e., deposition time is increased).
In consideration of this, it has been suggested to employ a method for depositing a functionally gradient thin film having a concentration gradient of an elemental composition along a thickness direction of the thin film using the plasma CVD device including the pair of first and second parallel-plate electrodes 2 and 3.
For example, Japanese Laid-Open Patent Publication No. 2000-192246 discloses a method for depositing the functionally gradient thin film by providing two or more types of different reaction gasses in a plasma space while sequentially varying their mixing ratio. Further, Japanese Laid-Open Patent Publication No. 7-169697 discloses a method for depositing the functionally gradient thin film having a concentration gradient along a thickness direction of the thin film by varying a flow rate of the carrier gas, Japanese Laid-Open Patent Publication No. 2000-144434 discloses a method for depositing the functionally gradient thin film having a concentration gradient along a thickness direction of the thin film by sequentially varying a value of a voltage or a frequency of the high-frequency power applied to an electrode by a high-frequency power source during a thin film deposition process, and Japanese Laid-Open Patent Publication No. 2000-204475 discloses a method for depositing the functionally gradient thin film having a concentration gradient along a thickness direction of the thin film by sequentially varying a temperature of the substrate.
However, in such a method which controls parameters for the thin film deposition, it is not easy to accurately control the parameters. Further in the film deposition process, quality of the portions of the film varies according to variations of the parameters and there is a time lag between a variation of the parameters and a variation of the quality, and therefore differences in quality among the portions of the film are caused.
According to another aspect of the present invention, there is provided a method for depositing a functionally gradient thin film comprising the steps of: providing a substrate on which a thin film is deposited in a process chamber which includes a cylindrical rotary electrode opposed to a substrate, the cylindrical rotary electrode being rotated by applying high-frequency power thereto; introducing two or more types of material gases into the process chamber; performing a first film deposition by rotating the cylindrical rotary electrode so as to form plasma between the cylindrical rotary electrode and the substrate for depositing the first thin film while sliding the substrate into the process chamber along a first sliding direction which is identical or opposite to a rotation direction of the cylindrical rotary electrode; and performing a second film deposition after the first film deposition by sliding the substrate along a second sliding direction opposite to the first sliding direction.
In one embodiment of this invention, the substrate is slid along a rotation direction of the cylindrical rotary electrode through a plasma space in which the plasma is created between the cylindrical rotary electrode and the substrate.
In one embodiment of this invention, the substrate is slid along a direction opposite to the rotation direction of the cylindrical rotary electrode through the plasma space in which the plasma is created between the cylindrical rotary electrode and the substrate.
In one embodiment of this invention, a thin film is deposited on the substrate under fixed conditions from a beginning to an end of the film deposition process.
In one embodiment of this invention, the fixed conditions include concentrations related to concentrations of the material gases in the process chamber, the high-frequency power applied to the cylindrical rotary electrode so as to create the plasma, a size of a gap between the cylindrical rotary electrode and the substrate, a number of rotations per amount of time of the cylindrical rotary electrode, a temperature of the substrate, and a sliding speed of the substrate.
According to another aspect of the present invention, there is provided a method for depositing a functionally gradient thin film comprising the steps of: providing a substrate on which a thin film is deposited in a process chamber which includes a cylindrical rotary electrode opposed to the cylindrical rotary electrode, the cylindrical rotary electrode being rotated by applying high-frequency power thereto; introducing two or more types of material gases into the process chamber; performing a first film deposition by rotating the cylindrical rotary electrode so as to form plasma between the cylindrical rotary electrode and the substrate for depositing the first thin film while sliding the substrate into the process chamber along a first sliding direction which is identical or opposite to a rotation direction of the cylindrical rotary electrode; and performing a second film deposition after the first film deposition by sliding the substrate along a second sliding direction opposite to the first sliding direction.
According to still another aspect of the present invention, there is provided a method for depositing a functionally gradient thin film comprising the steps of: providing a plurality of process chambers connected to each other, each of the plurality of process chambers including a cylindrical rotary electrode being rotated by applying high-frequency power thereto; introducing two or more types of material gases having different dissociation energies into each of the plurality of process chambers; and depositing thin films by rotating the cylindrical rotary electrodes included in the plurality of process chambers along different directions while sliding a substrate on which the thin films are deposited through the plurality of process chambers along a prescribed direction so as to create plasma between the cylindrical rotary electrode and the substrate in each of the plurality of process chamber for depositing the films.
According to still another aspect of the present invention, there is provided a method for depositing a functionally gradient thin film comprising the steps of: providing a plurality of process chambers connected to each other, each of the plurality of process chambers including a cylindrical rotary electrode being rotated by applying high-frequency power thereto; introducing two or more types of material gases having substantially equivalent dissociation energies into at least one of the plurality of process chambers and introducing two or more types of material gases having different dissociation energies into at least one of the other process chambers; and depositing thin films by rotating the cylindrical rotary electrodes included in the plurality of process chambers along their respective prescribed directions while sliding a substrate on which the thin films are deposited through the plurality of process chambers along a prescribed direction so as to create plasma between the cylindrical rotary electrode and the substrate in each of the plurality of process chamber for depositing the films.
According to still another aspect of the present invention, there is provided a method for depositing a functionally gradient thin film comprising the steps of: providing a plurality of process chambers connected to each other, each of the plurality of process chambers including a cylindrical rotary electrode being rotated by applying high-frequency power thereto; introducing two or more types of material gases having substantially equivalent dissociation energies into at least one of the plurality of process chambers and introducing two or more types of material gases having different dissociation energies into at least one of the other process chambers; performing a first film deposition by rotating the cylindrical rotary electrodes included in the plurality of process chambers along their respective rotation directions while sliding a substrate through the plurality of process chambers along a first sliding direction which is a prescribed direction; and performing a second film deposition after the first film deposition by sliding the substrate along a second sliding direction opposite to the first sliding direction.
Thus, the invention described herein makes possible the advantages of providing: (1) a method for easily depositing a functionally gradient thin film having a concentration gradient along a thickness direction of the thin film; and (2) a method for depositing a functionally gradient thin film having an elemental composition in which different types of elements are complexly distributed along a thickness direction of the thin film and another functionally gradient thin film having an elemental composition in which a part of different types of elements is homogeneously distributed such that a composition ratio between the different types of elements is invariable.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.